Standardise template locations
Move CMSSettingsController class to SiteConfig module
Fix CMSMenu behaviour for namespaced admin sections
Split classes into one per file
Manual fixes and cleanup
Currently help menu item is the only external link in the CMS and the ability for it to work is hardcoded in the template. This request makes the target attribute definable by CMSMenu::add_link().
Adds documentation for how to add a basic external link to the CMS.